Region classification of film non-uniformity based on processing of substrate images

ABSTRACT

A method of classification of a film non-uniformity on a substrate includes obtaining a color image of a substrate with the color image comprising a plurality of color channels, obtaining a standard color for the color image of the substrate, for each respective pixel along a path in the color image determining a difference vector between the a color of the respective pixel and the standard color to generate a sequence of difference vectors, sorting the pixels along the path into a plurality of regions including at least one normal region and at least one abnormal region based on the sequence of difference vectors, and classifying the at least one abnormal region as overpolished or underpolished based on at least one difference vector of a pixel at a boundary between the abnormal region and an adjacent normal region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Application Ser. No.63/156,856, filed on Mar. 4, 2021, the disclosure of which isincorporated by reference.

TECHNICAL FIELD

This disclosure relates to optical metrology, e.g., techniques toclassify non-uniformity of a film on a substrate.

BACKGROUND

An integrated circuit is typically formed on a substrate by thesequential deposition of conductive, semiconductive, or insulativelayers on a silicon wafer. Planarization of a substrate surface may berequired for the removal of a filler layer or to improve planarity forphotolithography during fabrication of the integrated circuit.

Chemical mechanical polishing (CMP) is one accepted method ofplanarization. This planarization method typically requires that thesubstrate be mounted on a carrier or polishing head. The exposed surfaceof the substrate is typically placed against a rotating polishing pad.The carrier head provides a controllable load on the substrate to pushit against the polishing pad. An abrasive polishing slurry is typicallysupplied to the surface of the polishing pad.

Various optical metrology systems, e.g., spectrographic orellipsometric, can be used to measure the thickness of the substratelayer pre-polishing and post-polishing, e.g., at an in-line orstand-alone metrology station.

As a parallel issue, advancements in hardware resources such asGraphical Processing Units (GPU) and Tensor Processing Units (TPU) haveresulted in a vast improvement in the deep learning algorithms and theirapplications. One of the evolving fields of deep learning is computervision and image recognition. Such computer vision algorithms are mostlydesigned for image classification or segmentation.

SUMMARY

In one aspect, a method of classification of a film non-uniformity on asubstrate includes obtaining a color image of a substrate with the colorimage comprising a plurality of color channels, obtaining a standardcolor for the color image of the substrate, for each respective pixelalong a path in the color image determining a difference vector betweenthe a color of the respective pixel and the standard color to generate asequence of difference vectors, and sorting the pixels along the pathinto a plurality of regions including at least one normal region and atleast one abnormal region based on the sequence of difference vectors,including comparing a multiplicity of the difference vectors in thesequence to a threshold.

In another aspect, a computer program product can be provided toclassify the film.

In another aspect, a chemical mechanical polishing system includes acontrol system configured to classify the film.

Implementations can include one or more of the following potentialadvantages. Abnormalities in a film on a substrate, e.g., non-uniformityin thickness, and presence of residue or defects, can be analyzedquickly. In some implementations, abnormality in a film on a substratecan be analyzed quickly for die-to-die measurements. For example, anin-line metrology system can measure film abnormalities for a substratebased on color images of the substrate. The measured abnormality, e.g.,the measured non-uniformity, can be used to control polishing parametersto compensate for underpolishing and overpolishing of a substrate.

The described approach can use color values in a sequence of pixels todetect an abnormality in the film of a substrate and classify the typeof abnormality. A model can be trained to determine different types ofabnormalities based on color values.

The metrology system can have high inference speed and superiordetection and classification of non-uniform regions. The approach canalso take into consideration sublayer variation.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other aspects, featuresand advantages will be apparent from the description and drawings, andfrom the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a view of an example of an in-line opticalmeasurement system.

FIG. 2 illustrates a flow chat for a method of classifying anon-uniformity of a film on a substrate using computational approach.

FIG. 3A illustrates a mask being applied to an exemplary image of asubstrate used for computational analysis.

FIG. 3B illustrates graph of histograms of three color channels.

FIGS. 4A-4C illustrate an example of exemplary image of a substrate witha radial profile and results of non-uniformity analysis.

FIGS. 5A-5C illustrate another example of exemplary image of a substratewith a radial profile and results of non-uniformity analysis.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Thin-film thickness measurements from dry metrology systems are used inCMP processing because of the variability in the polishing rate thatoccurs in CMP processes. Such dry metrology measurement techniques oftenuse a spectrographic or ellipsometric approach in which variables in anoptical model of a film stack are fit to the collected measurements.Such measurement techniques typically require precise alignment of asensor to a measurement spot of the substrate to ensure that the modelis applicable to the collected measurements. Therefore, measuring alarge number of points on the substrate can be time-consuming, andclassification of the type and the degree of under- and over-polishingmight not be feasible as imposing an unacceptable reduction inthroughput.

However, an image processing technique based on color images can providefaster detection of abnormalities on the substrate and classification ofthe type of abnormality with satisfactory accuracy. In particular, thecolor images of dies from a substrate can be divided into multipleregions. Each region can be divided into multiple areas of the same orsimilar color. For example, a pixel with a color vector that issufficiently close to a target vector can be classified as properlypolished; pixels that fail the test can be classified as abnormality. Inone implementation, for each of a plurality of paths across thesubstrate, the color of each pixel along the path can be analyzed, andthe type and the degree of abnormality can be determined based on thesequence of vectors in color space for pixels at the boundary betweenthe properly polished regions and improperly polished regions along thepath. For example, whether regions are over-polished or under-polishedrelative to other regions, and the degree of over-polishing orunder-polishing, can be determined based on the vectors.

Referring to FIG. 1, a polishing apparatus 100 includes one or morecarrier heads 126, each of which is configured to carry a substrate 10,one or more polishing stations 106, and a transfer station to loadsubstrate to and unload substrates from a carrier head. Each polishingstation 106 includes a polishing pad 130 supported on a platen 120. Thepolishing pad 130 can be a two-layer polishing pad with an outerpolishing layer and a softer backing layer.

The carrier heads 126 can be suspended from a support 128, and movablebetween the polishing stations. In some implementations, the support 128is an overhead track and each carrier head 126 is coupled to a carriage108 that is mounted to the track so that each carriage 108 can beselectively moved between the polishing stations 124 and the transferstation. Alternatively, in some implementations, the support 128 is arotatable carousel, and rotation of the carousel moves the carrier heads126 simultaneously along a circular path.

Each polishing station 106 of the polishing apparatus 100 can include aport, e.g., at the end of an arm 134, to dispense polishing liquid 136,such as abrasive slurry, onto the polishing pad 130. Each polishingstation 106 of the polishing apparatus 100 can also include padconditioning apparatus to abrade the polishing pad 130 to maintain thepolishing pad 130 in a consistent abrasive state.

Each carrier head 126 is operable to hold a substrate 10 against thepolishing pad 130. Each carrier head 126 can have independent control ofthe polishing parameters, for example, pressure associated with eachrespective substrate. In particular, each carrier head 126 can include aretaining ring 142 to retain the substrate 10 below a flexible membrane144. Each carrier head 126 can also include a plurality of independentlycontrollable pressurizable chambers defined by the membrane, e.g., threechambers 146 a-146 c, which can apply independently controllablepressures to associated zones on the flexible membrane 144 and thus onthe substrate 10. Although only three chambers are illustrated in FIG. 1for ease of illustration, there could be one or two chambers, or four ormore chambers, e.g., five chambers.

Each carrier head 126 is suspended from the support 128 and is connectedby a drive shaft 154 to a carrier head rotation motor 156 so that thecarrier head can rotate about an axis 127. Optionally each carrier head126 can oscillate laterally, e.g., by driving the carriage 108 on atrack, or by the rotational oscillation of the carousel itself. Inoperation, the platen is rotated about its central axis, and eachcarrier head is rotated about its central axis 127 and translatedlaterally across the top surface of the polishing pad.

A controller 190, such as a programmable computer, provides a controlsystem. The controller 190 is connected to each motor to independentlycontrol the rotation rate of the platen 120 and the carrier heads 126.The controller 190 can include a central processing unit (CPU), amemory, and support circuits, e.g., input/output circuitry, powersupplies, clock circuits, cache, and the like. The memory is connectedto the CPU. The memory is a non-transitory computable readable medium,and can be one or more readily available memory such as random accessmemory (RAM), read-only memory (ROM), floppy disk, hard disk, or anotherform of digital storage. In addition, although illustrated as a singlecomputer, the controller 190 could be a distributed system, e.g.,including multiple independently operating processors and memories.

The polishing apparatus 100 also includes an in-line (also referred toas in-sequence) optical metrology system 160. A color imaging system ofthe in-line optical metrology system 160 is positioned within thepolishing apparatus 100, but does not perform measurements during thepolishing operation; rather measurements are collected between polishingoperations, e.g., while the substrate is being moved from one polishingstation to another, or pre- or post-polishing, e.g., while the substrateis being moved from the transfer station to a polishing station or viceversa. In addition, the in-line optical metrology system 160 can bepositioned in a fab interface unit or a module accessible from the fabinterface unit to measure a substrate after the substrate is extractedfrom a cassette but before the substrate is moved to the polishing unit,or after the substrate has been cleaned but before the substrate isreturned to the cassette.

The in-line optical metrology system 160 includes a sensor assembly 161that provides the color imaging of the substrate 10. The sensor assembly161 can include a light source 162, a light detector 164, and circuitry166 for sending and receiving signals between the controller 190 and thelight source 162 and light detector 164.

The light source 162 can be operable to emit white light. In oneimplementation, the white light emitted includes light havingwavelengths of 200-800 nanometers. A suitable light source is an arrayof white-light light-emitting diodes (LEDs), or a xenon lamp or a xenonmercury lamp. The light source 162 is oriented to direct light 168 ontothe exposed surface of the substrate 10 at a non-zero angle of incidencea. The angle of incidence a can be, for example, about 30° to 75°, e.g.,50°.

The light source can illuminate a substantially linear elongated regionthat spans the width of the substrate 10. For example, the light source162 can include optics, e.g., a beam expander, to spread the light fromthe light source into an elongated region. Alternatively or in addition,the light source 162 can include a linear array of light sources. Thelight source 162 itself, and the region illuminated on the substrate,can elongate and have a longitudinal axis parallel to the surface of thesubstrate.

A diffuser 170 can be placed in the path of the light 168, or the lightsource 162 can include a diffuser, to diffuse the light before itreaches the substrate 10.

The detector 164 is a color camera that is sensitive to light from thelight source 162. The camera includes an array of detector elements. Forexample, the camera can include a CCD array. In some implementations,the array is a single row of detector elements. For example, the cameracan be a line-scan camera. The row of detector elements can extendparallel to the longitudinal axis of the elongated region illuminated bythe light source 162. Where the light source 162 includes a row oflight-emitting elements, the row of detector elements can extend along afirst axis parallel to the longitudinal axis of the light source 162. Arow of detector elements can include 1024 or more elements.

The camera 164 is configured with appropriate focusing optics 172 toproject a field of view of the substrate onto the array of detectorelements. The field of view can be long enough to view the entire widthof the substrate 10, e.g., 150 to 300 mm long.

The camera 164, including associated optics 172, can be configured suchthat individual pixels correspond to a region having a length equal toor less than about 0.5 mm. For example, assuming that the field of viewis about 200 mm long and the detector 164 includes 1024 elements, thenan image generated by the line-scan camera can have pixels with a lengthof about 0.5 mm. To determine the length resolution of the image, thelength of the field of view (FOV) can be divided by the number of pixelsonto which the FOV is imaged to arrive at a length resolution.

The camera 164 can be also be configured such that the pixel width iscomparable to the pixel length. For example, an advantage of a line-scancamera is its very fast frame rate. The frame rate can be at least 5kHz. The frame rate can be set at a frequency such that as the imagedarea scans across the substrate 10, the pixel width is comparable to thepixel length, e.g., equal to or less than about 0.3 mm.

The light source 162 and the light detector 164 can be supported on astage 180. Where the light detector 164 is a line-scan camera, the lightsource 162 and camera 164 are movable relative to the substrate 10 suchthat the imaged area can scan across the length of the substrate. Inparticular, the relative motion can be in a direction parallel to thesurface of the substrate 10 and perpendicular to the row of detectorelements of the line-scan camera 164.

In some implementations, the stage 182 is stationary, and the supportfor the substrate moves. For example, the carrier head 126 can move,e.g., either by motion of the carriage 108 or by rotational oscillationof the carousel, or the robot arm holding the substrate in a factoryinterface unit can move the substrate 10 past the line-scan camera 182.In some implementations, the stage 180 is movable while the carrier heador robot arm remains stationary for the image acquisition. For example,the stage 180 can be movable along a rail 184 by a linear actuator 182.In either case, this permits the light source 162 and camera 164 to stayin a fixed position relative to each other as the area being scannedmoves across the substrate 10.

A possible advantage of having a line-scan camera and light source thatmove together across the substrate is that, e.g., as compared to aconventional 2D camera, the relative angle between the light source andthe camera remains constant for different positions across the wafer.Consequently, artifacts caused by variation in the viewing angle can bereduced or eliminated. In addition, a line scan camera can eliminateperspective distortion, whereas a conventional 2D camera exhibitsinherent perspective distortion, which then needs to be corrected by animage transformation.

The sensor assembly 161 can include a mechanism to adjust verticaldistance between the substrate 10 and the light source 162 and detector164. For example, the sensor assembly 161 can include an actuator toadjust the vertical position of the stage 180.

Optionally a polarizing filter 174 can be positioned in the path of thelight, e.g., between the substrate 10 and the detector 164. Thepolarizing filter 174 can be a circular polarizer (CPL). A typical CPLis a combination of a linear polarizer and quarter-wave plate. Properorientation of the polarizing axis of the polarizing filter 174 canreduce haze in the image and sharpen or enhance desirable visualfeatures.

Assuming that the outermost layer on the substrate is a semitransparentlayer, e.g., a dielectric layer, the color of light detected at detector164 depends on, e.g., the composition of the substrate surface,substrate surface smoothness, and/or the amount of interference betweenlight reflected from different interfaces of one or more layers (e.g.,dielectric layers) on the substrate. As noted above, the light source162 and light detector 164 can be connected to a computing device, e.g.,the controller 190, operable to control their operation and receivetheir signals. The computing device that performs the various functionsto convert the color image to a thickness measurement, can be consideredpart of the metrology system 160.

FIG. 2 illustrates a method 200 of image processing for use in detectingand classifying abnormality in a film on a substrate. The method can beperformed by the controller 190. The controller 190 receives a colorimage of the substrate. The color images can be RGB images, or images inanother color space, e.g., XYZ or HCL.

The controller executes an image processing algorithm that processes thecolor images. The controller assembles individual image lines from thelight detector 164 into a two-dimensional color image (step 205). Thecontroller can apply an offset and/or a gain adjustment to the intensityvalues of the pixels in the image in each color channel (step 210). Eachcolor channel can have a different offset and/or gain. Optionally, theimage can be normalized (step 215). For example, the difference betweenthe measured image and a standard predefined image can be calculated.For example, the controller can store a background image for each of thered, green, and blue color channels, and the background image can besubtracted from the measured image for each color channel. The image canalso be transformed, e.g., scaled and/or rotated and/or translated, intoa standard image coordinate frame (step 220). For example, the image canbe translated so that the substrate center is at the center point of theimage and/or the image can be scaled so that the edge of the substrateis at the edge of the image, and/or the image can be rotated so thatthere is a Wangle between the x-axis of the image and the radial segmentconnecting the substrate center and the substrate orientation feature,e.g., the notch or flat of the wafer. The substrate orientation can bedetermined by a notch finder, or by image processing of the color image320, e.g., to determine the angle of scribe lines in the image. Thesubstrate position can also be determined by image processing of thecolor image 320, e.g., by detecting the circular substrate edge and thendetermining a center of the circle.

A mask can be applied to image 320. The mask can eliminate unwantedpixels, e.g., pixels from the portions of the substrate corresponding tothe scribe lines, from the computation. As an example, the controller190 can store a die mask that identifies a location and area of interestin the image. For example, for rectangular regions, the area can bedefined by upper right and lower left coordinates in the image. Thus,the mask could be a data file that includes a pair of an upper right anda lower left coordinate for each region. In other cases, where regionsare non-rectangular, more complex functions can be used. In someimplementations, substrate orientation and position can be determined,and the die mask can be aligned with respect to the image.

Referring to FIG. 3, an example of an image 300 of a substrate 10 iscollected with in-line optical metrology system 160 is shown. Thein-line optical metrology system 160 produces a color image 300 with atleast three color channels, e.g., RGB channels. The image can be ahigh-resolution image, e.g., an image of at least 720x1080 pixelshigh-resolution, although lower resolution, e.g., down to 150x150pixels, or higher resolution, can be used. The color at any particularpixel depends on the thickness of one or more layers, including the toplayer, in the area of the substrate corresponding to the pixel.

The then algorithm determines the a “uniform color” for the unmaskedportion of the image (step 225). In some implementations, an intensityhistogram is determined for each color channel, and the algorithm findsthe peak in each of the three histograms (R, G, and B planes). The tupleof intensity values from the peaks in the histograms provides a colorvalue. This color value is termed the “uniform color” (UC) of the image300.

For example, FIG. 3B illustrates histograms 360, 370, 380 for the red,green and blue channels respectively, and the peaks at R1, G1 and B1 foreach histogram. The tuple (R1, G1, B1) provides the uniform color.However, other techniques could be used to define a uniform color, e.g.,simply calculating a mode value or mean value for each channel.

The color images collected can be stored as PNG images for furtheranalysis or processing, although many other formats, e.g., JPEG, etc.,are possible.

Returning to FIG. 2, the masked image can be fed into the imageprocessing algorithm. The controller can store data defining a pluralityof paths across the image. For example, the paths can be lines extendingradially outward from the center of the substrate (see FIG. 4A),although other paths are possible. For radial lines, the lines canpositioned at equal angular intervals, e.g., 1-10°, around the center ofthe substrate.

For each path, the controller computes the difference vector (DV)between each pixel in the sequence of pixels along the path and theuniform color (UC) (step 230). The difference vector can be representedas a tuple, e.g., (D_(R), D_(G), D_(B)). The difference vector of thepixels can be represented either by Cartesian or by sphericalcoordinates within the computation algorithm as shown below:

DV=(D _(r) ,D _(g) ,D _(b)) where

D _(X) =X−PPMEAN_(X) where X=R, G, or B  (Cartesian Coordinates)

DV=(ρ,Θ,ϕ) where

ρ=√{square root over (D _(r) ² +D _(g) ² +D _(b) ²)}

θ=tan⁻¹(D _(g) /D _(r))

φ=tan⁻¹(D _(b) /S)  (Spherical Coordinates)

where S=√{square root over (D_(r) ²+D_(g) ²)} is the projection of DVonto (RG) plane.

The sequence of difference vectors along a particular path provide adifference vector profile. Each difference vector profile is analyzed todetect regions or segments along the radial profile that are non-uniform(step 240).

In some implementations, uniform regions are distinguished fromnon-uniform regions by using a threshold value. Pixels for which amagnitude of the difference vector (e.g., calculated as conventionalEuclidian distance) is above the threshold value are classified as“non-uniform.” In contrast, pixels for which a magnitude of thedifference vector is below the threshold value are classified as“uniform.” In some implementations, the region interpretation can be setautomatically by using machine learning.

In some implementations, the controller established four possibleclassifications for a pixel: properly polished (type 1), underpolished(type 2), over-polished (type 3), or non-uniformly polished butunclassified or anomalous (type 4).

The algorithm first divides the path into groups of contiguous properlypolished pixels and groups of contiguous unclassified pixels. For aselected pixel if the prior pixel was properly polished, but a magnitudeof the difference vector (MagDV) is greater than the threshold value,then a new non-uniform region (i.e., nonPP or type4) region isidentified. The algorithm continues to group pixels along the path intothe identified non-uniform region until a number of sequential properlypolished pixels are encountered. By repeating this process along thepath, the pixels are divided into groups of normal pixels and groups ofabnormal pixels. An “nSustain” parameter can be used as a noise filterto determine how long a sequence of adjacent pixels is required to starta region of a new type. For example, if a type1 (i.e. normal pixel)region is shorter than the nSustain parameter value, then those type1pixels are assigned to the adjacent region of type 4 (i.e. not normalpixels.

Having divided the pixels along the path into groups, the type ofabnormality, e.g., underpolished (type 2) or overpolished (type 3), canclassified for each group (step 250). The type of abnormality can bedetermined by examining the difference vectors, and in particular thedifference vectors at the start of a group of abnormal pixels. Withoutbeing limited to any particular theory, although color values at thecenter of a non-uniform region can match, the transition from a PPregion to an under-polished (i.e., UP or type2) region can be differentthat the transition from a PP region to an over-polished (i.e., OPtype3) region.

In some implementations, a value F is calculated based on the ratio ofdifferences in certain color channels. For example, F can be calculatedbased on a sum of a first ratio of differences in two color channels anda second ratio of differences in two color channels. The value F canthen be compared to one or two threshold values to determine to whetherthe region is underpolished (type 2) or overpolished (type 3). If the Fdoes not satisfy either threshold, then the region can be identified asan anomaly, e.g., remain type 4.

In some implementations, F and the type of abnormality is determinedaccording to the following function:

${RGBSeqRatio} = {F = {\frac{D_{g}}{D_{r}} + {\frac{D_{b}}{D_{r}}\mspace{31mu}\begin{matrix}{{If}\mspace{14mu}( {F > {{FT}\; 1}} )\mspace{14mu}{Then}\mspace{14mu}{Type}\; 2({UP})} \\{{Else}\mspace{14mu}{if}\mspace{14mu}( {F < {{FT}\; 2}} )\mspace{14mu}{Then}\mspace{14mu}{Type}\; 2({OP})} \\{{Else}\mspace{14mu}{Anomaly}}\end{matrix}}}}$

where D_(R), D_(G) and D_(B) are the difference values for the red,green and blue color channels, and FT1 and FT2 are empiricallydetermined threshold values.

A preset number of pixels in a nonPP region that are sequential alongthe path beginning at a neighboring PP region are evaluated. The presetnumber of pixels can be selected by a user, e.g., by user input. Theclassification sequence is performed by looking at 3-10 pixels, e.g.,3-5 pixels (e.g., one region can be 50-60 pixels wide) and computing theratio of differences. For example, for each pixel in a sequence of Npixels, the controller computes the factor (F) to provide F1, F2, F3, .. . , FN. Each calculated F, i.e., F1, F2, F3, . . . , FN, is comparedto each threshold values FT1, FT2, . . . , FTn. If all pixels satisfythe same condition, e.g., F1, FN are all less than FT1 or are allgreater than FT2, then the region is classified as “overpolished” or“underpolished.” Otherwise it is classified as an unclassifiednon-uniformity or abnormality.

In another implementation, the interpretation between underpolished oroverpolished can be evaluated using spherical coordinate angles (e.g., Θand ϕ) of the DV points in type 4 regions (i.e., the points that areadjacent to the neighboring type 1 region). Therefore, the sequence fordetermining UP or OP is a) set upper and lower thresholds for Θ and ϕfor UP behavior; b) analyze several PP adjacent points in the type4region; and c) if Θ and ϕ fall within the type2 ranges then classify astype 2 else, classify as type3.

Based on the computed data the “non-uniformity” can be furtherclassified (step 250) by type (step 250 a) and by severity (step 250 b).Similarly as in the previous steps, the color image is inputted into theimage-processing algorithm and divided into volumes then DV is computedfor each volume. For each non-uniform region the severity is determinedby quasi-quantitative description such as “mild”, “moderate”, or“severe.” This is executed for each radial profile by transforming setsof RGB pixels in the non-uniform region to the rg chromaticity space.Then the area of the bounding rectangle (BRA) of the non-uniform pixelsequence in the rg space is computed. Then the BRA is compared to areasof thresholds to determine the level of severity. For example, if thereare two thresholds A1 and A2 with A1<A2, if BRA is less then A1, thenclassify as “mild”. If BRA is between A1 and A2, then classify as“moderate”. If BRA is greater than A2, then classify as “severe”. Asdescribed, there are only three categories listed however, the algorithmcan have more or less than three categories based on the number of thearea thresholds.

As another method of determining severity, an arc length of the rgsequence can be computed (instead of the BRA). This may be moredifficult, although should be in correspondence to the underlyingtheory. However, computation of the bounding rectangle iscomputationally easier and appears sufficient for accuracy.

Referring to FIGS. 4A-4C, a first example of an exemplary image 400 of asubstrate with a radial profile is illustrated showing non-uniformregions 402 and 404 with “severe” level of abnormality. The severe levelis classified and presented by data in chart shown in FIG. 4B. The line408 indicates threshold level the data above 412 the threshold line 408is non-uniform and the data below 410 the threshold line 408 is uniform.The size of the BRA area is computed and presented in FIG. 4C confirmingthe severe non-uniformity of this radial profile 400.

FIGS. 5A-5C illustrate another example of exemplary image 500 of asubstrate with a radial profile showing a case of mild to moderatenon-uniformity.

In general, data can be used to control one or more operation parametersof the CMP apparatus. Operational parameters include, for example,platen rotational velocity, substrate rotational velocity, the polishingpath of the substrate, the substrate speed across the plate, thepressure exerted on the substrate, slurry composition, slurry flow rate,and temperature at the substrate surface. Operational parameters can becontrolled real-time and can be automatically adjusted without the needfor further human intervention.

As used in the instant specification, the term substrate can include,for example, a product substrate (e.g., which includes multiple memoryor processor dies), a test substrate, a bare substrate, and a gatingsubstrate. The substrate can be at various stages of integrated circuitfabrication, e.g., the substrate can be a bare wafer, or it can includeone or more deposited and/or patterned layers. The term substrate caninclude circular disks and rectangular sheets.

Embodiments of the invention and all of the functional operationsdescribed in this specification can be implemented in digital electroniccircuitry, or in computer software, firmware, or hardware, including thestructural means disclosed in this specification and structuralequivalents thereof, or in combinations of them.

Embodiments of the invention can be implemented as one or more computerprogram products, i.e., one or more computer programs tangibly embodiedin a non-transitory machine readable storage media, for execution by, orto control the operation of, data processing apparatus, e.g., aprogrammable processor, a computer, or multiple processors or computers.

Terms of relative positioning are used to denote positioning ofcomponents of the system relative to each other, not necessarily withrespect to gravity; it should be understood that the polishing surfaceand substrate can be held in a vertical orientation or some otherorientations.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made. For example

-   -   Rather than a line scan camera, a camera that images the entire        substrate could be used. In this case, motion of the camera        relative to the substrate is not needed.    -   The camera could cover less than the entire width of the        substrate. In this case, the camera would need to undergo motion        in two perpendicular directions, e.g., be supported on an X-Y        stage, in order to scan the entire substrate.    -   The light source could illuminate the entire substrate. In this        case, the light source need not move relative to the substrate.    -   The light detector can be a spectrometer rather than a color        camera; the spectra data can then be reduced to the RGB color        space.    -   The sensory assembly need not an in-line system positioned        between polishing stations or between a polishing station and a        transfer station. For example, the sensor assembly could be        positioned within the transfer station, positioned in a cassette        interface unit, or be a stand-alone system.

Accordingly, other implementations are within the scope of the claims.

What is claimed is:
 1. A non-transitory computer readable mediumcomprising a computer program to classify a film non-uniformity on asubstrate, the computer program including instructions to cause one ormore computers to: obtain a color image of a substrate, the color imagecomprising a plurality of color channels; obtain a standard color forthe color image of the substrate; for each respective pixel along a pathin the color image, determine a difference vector between the a color ofthe respective pixel and the standard color to generate a sequence ofdifference vectors; and classify the pixels along the path as normal orabnormal based on the sequence of difference vectors; sort the pixelsinto one or more regions in response to the pixels being identified asnormal or abnormal; and classify a region having abnormal pixels asoverpolished or underpolished based on at least one difference vector ofa pixel at a boundary between the region having abnormal pixels and anadjacent region having normal pixels.
 2. The computer readable medium ofclaim 1, comprising instructions to classify the abnormal region asoverpolished or underpolished based a multiplicity of difference vectorsfor each of a multiplicity of successive pixels along the path at theboundary.
 3. The computer readable medium of claim 2, wherein themultiplicity of successive pixels is no more than 5 pixels.
 4. Thecomputer readable medium of claim 2, comprising instructions to classifythe abnormal region as overpolished or underpolished based on each ofthe multiplicity of difference vectors meeting a criterion.
 5. Thecomputer readable medium of claim 2, wherein the instructions toclassify the abnormal region as overpolished or underpolished includeinstructions to calculate a factor based on a ratio of difference valuesin two color channels.
 6. The computer readable medium of claim 5,wherein the instructions to calculate the factor include instructions tocalculate a sum of a first ratio of difference values in a first twocolor channels and a second ratio of difference values in a second twocolor channels.
 7. The computer readable medium of claim 5, wherein theinstructions to classify the abnormal region as overpolished orunderpolished regions include instructions to compare the factor to atleast a third threshold value.
 8. The computer readable medium of claim7, comprising instructions to classify the abnormal region asunderpolished in response to determining that the factor exceeds thethird threshold value.
 9. The computer readable medium of claim 7,comprising instructions to classify the abnormal region as overpolishedin response to determining that the factor does not exceeds a fourththreshold value.
 10. The computer readable medium of claim 6, whereinthe first two color channels are green and red and the second two colorchannels are blue and red.
 11. The computer readable medium of claim 1,comprising instructions to determine a severity of the abnormal regionbased on the multiplicity of the difference vectors.
 12. The computerreadable medium of claim 10, wherein determining the severity comprisesdetermining a minimum bounding region containing the difference vectorsfor the pixels in the abnormal region in a color space at least two ofthe color channels, and comparing an area of the bounding region to afifth threshold value.
 13. The computer readable medium of claim 11,wherein the minimum bounding region comprises a rectangle.
 14. A methodof classification of a film non-uniformity on a substrate, comprising:obtaining a color image of a substrate, the color image comprising aplurality of color channels; obtaining a standard color for the colorimage of the substrate; for each respective pixel along a path in thecolor image, determining a difference vector between the a color of therespective pixel and the standard color to generate a sequence ofdifference vectors; sorting the pixels along the path into a pluralityof regions including at least one normal region and at least oneabnormal region based on the sequence of difference vectors; andclassifying the at least one abnormal region as overpolished orunderpolished based on at least one difference vector of a pixel at aboundary between the abnormal region and an adjacent normal region. 15.The method medium of claim 14, wherein obtaining the color imageincludes scanning the substrate with an in-line metrology systemincluding a line-scan imager.
 16. A polishing system, comprising: apolisher to polish a substrate; an in-line metrology system to obtain tocolor image of a substrate, the color image comprising a plurality ofcolor channels; and a controller configured to receive obtain the colorimage from the in-line metrology system, obtaining a standard color forthe color image of the substrate, for each respective pixel along a pathin the color image, determine a difference vector between the a color ofthe respective pixel and the standard color to generate a sequence ofdifference vectors, classify the pixels along the path as normal orabnormal based on the sequence of difference vectors, sort the pixelsinto one or more regions in response to the pixels being identified asnormal or abnormal, classify a region having abnormal pixels asoverpolished or underpolished based on at least one difference vector ofa pixel at a boundary between the region having normal pixels and anadjacent region having normal pixels, and adjust a polishing parameterof the polisher for a region having pixels identified as abnormal basedon the region being classified as overpolished or underpolished.
 17. Thepolishing system of claim 16, wherein the controller is configured toclassify the region as overpolished or underpolished based amultiplicity of difference vectors for each of a multiplicity ofsuccessive pixels along the path at the boundary.
 18. The polishingsystem of claim 17, wherein the controller is configure to classify theregion as overpolished or underpolished based on each of themultiplicity of difference vectors meeting a criterion.
 19. Thepolishing system of claim 16, wherein the controller is configured todetermine a severity of the region having abnormal pixels based on themultiplicity of the difference vectors.
 20. The polishing system ofclaim 19, wherein the controller is configure to determine the severityby determining a minimum bounding region containing the differencevectors for the pixels in the abnormal region in a color space at leasttwo of the color channels, and comparing an area of the bounding regionto a fifth threshold value.